The present invention relates to a fuel supply system for an internal combustion engine.
As a prior art, there has been proposed a system that aims to decrease adhesion of the fuel on the suction air passage and suction valve, by heating and gasifying the fuel injected by a fuel injection valve with a heater installed in a suction air passage, so as to particularly improve combustion at cold start-up and reduce hazardous hydrocarbon exhaust. As in a U.S. Pat. No. 5,894,832, for example, there has been a system having a composition where, in addition to a fuel injection valve (port fuel injection valve) installed near a suction port of each cylinder, a fuel injection valve (upstream fuel injection valve) and a heater are installed in an auxiliary air passage bypassing a throttle valve, aiming to prevent adhesion of the fuel on the suction air passage and improve combustion by injecting fuel onto the heater in the warming-up process after cold start-up so as to facilitate gasification of the fuel with the heater. Since gasification of the fuel is effective for improving combustion, the above known art has an advantage that hazardous hydrocarbon exhaust after cold start-up can be reduced by heating and gasifying fuel with the heater during idling after start-up as well as by setting the delay angle of ignition timing greater than in a conventional engine equipped with no heater so as to increase the exhaust temperature and accelerate the activity of catalysts.
In the above-mentioned U.S. patent, however, there remains a problem that, because almost all fuel injected is adhered onto the heater, a large capacity heater is needed for gasification and therefore power consumption increases and, further, a larger size heater is needed.
It is generally known that, if fuel is atomized into a particle size of about 10 microns, fuel particles can be carried by air flow and accordingly the fuel can be carried into the cylinder without adhesion on the suction air passage. For this reason, if an air-assist type high-atomizing injection valve is employed as the fuel injection valve installed in the upstream so as to let the fuel flow directly into the cylinder, heater can be eliminated from the composition of a system. If some fuel still adheres on the suction air passage due to unevenness of the fuel particles of the high-atomizing injection valve, it will be possible to compose a system where part of the fuel is let directly into the cylinder and the rest is adhered on the heater so as to decrease adhesion of the fuel on the suction air passage and decrease the power consumption of the heater accordingly.
With a system where the afore-mentioned air-assist type high-atomizing injection valve is employed in order to decrease the adhesion of the fuel on the suction air passage so as to eliminate the heater or decrease the power consumption of the motor consequently, however, there still remains a problem as follows. That is, the air-assist type injection valve takes in the air for fuel atomization from the upstream of the throttle valve but, because the pressure differential between the upstream of the throttle valve and the suction air passage in the downstream of the injection valve becomes lower during the start-up cranking, the air volume for fuel atomization decreases and atomization is not facilitated, and consequently fuel particles of larger sizes adhere on the suction air passage. As a result, flow of the fuel into the cylinder delays and start-up performance worsens. Besides, a lot of unburnt gas is exhausted until complete explosion because it takes a longer time for the inflow fuel into the cylinder to reach a certain quantity enough for stable combustion.
With a system equipped with a heater, there remains another problem that gasification of the fuel on the heater is not facilitated resulting from decreased airflow rate through the heater and higher pressure through the suction air passage during the start-up cranking, and consequently, start-up performance worsens and a lot of unburnt gas is exhausted.
Besides, because the pressure differential between upstream of the throttle valve and the suction air passage in the downstream of the injection valve becomes lower under a condition where the suction air passage pressure increases like in acceleration, the air for fuel atomization of the air-assist type injection valve becomes short and consequently fuel atomization is not facilitated. As a result, the amount of the fuel adhering on the suction air passage increases and accordingly the amount of the fuel flowing into the cylinder decreases, resulting in combustion worsening and hazardous gas exhaust.
The composition of the present invention for solving the above problem is shown in FIG. 1.
The first composition of the present invention is a fuel supply system for an internal combustion engine, which is equipped with a port fuel injection valve 2 installed near a suction port of each cylinder and an air-assist type upstream fuel injection valve 3, installed in a suction air passage in the upstream of the port fuel injection valve 2 or in an auxiliary air passage bypassing a throttle valve, that facilitates atomization of the fuel by introducing air into or near a fuel injection port; and also equipped with an injection controlling means 1 that injects fuel during the start-up cranking at least by the port fuel injection valve 2 and injects fuel as well after start-up at least by the upstream fuel injection valve 3.
The second composition of the present invention is a fuel supply system for an internal combustion engine, which is equipped with a port fuel injection valve 2 installed near a suction port of each cylinder; an upstream fuel injection valve 3 installed in a suction air passage in the upstream of the port fuel injection valve or in an auxiliary air passage bypassing a throttle valve; a heater part 4, installed in the injection direction of the upstream fuel injection valve 3, that gasifies whole or part of the injection fuel of the upstream fuel injection valve by heating; and a heater controlling means 5 that energizes the heater part; and also equipped with an injection controlling means 1 that injects fuel during the start-up cranking at least by the port fuel injection valve 2 and injects fuel as well at least by the upstream fuel injection valve 3 when and after the engine rotation speed exceeds a specified value, or when and after the suction air passage pressure becomes lower than a specified value, or when and after a detected suction air volume exceeds a specified value.
The third composition of the present invention is a fuel supply system for an internal combustion engine, which is equipped with a port fuel injection valve 2 installed near a suction port of each cylinder and an air-assist type upstream fuel injection valve 3, installed in a suction air passage in the upstream of the port fuel injection valve 2 or in an auxiliary air passage bypassing a throttle valve, that facilitates atomization of the fuel by introducing air into or near a fuel injection port; and also equipped with an injection controlling means that varies the injection quantity ratio of the port fuel injection valve 2 to the upstream fuel injection valve 3.